A pregnant woman and at least two others were injured Tuesday in an explosion at a motel in a suburb of Oklahoma City, authorities said.

The woman, who is eight months pregnant, and a man were critically injured in the blast at the Guest Inn Motel in Yukon about 6 p.m., police spokeswoman Klare Ly said. Another person was treated at the scene, according to the Emergency Medical Services Authority.

Ly said a couple other people may have suffered minor injuries.

The cause of the blast wasn't immediately known, but Ly said officials do not believe it was from a methamphetamine lab.

"The walls were blown out and debris is across the parking lot," Ly said. At least eight of the motel's units were damaged, she said.

The pregnant woman, who is the motel's manager, suffered burns to her hands, face, lips and ears, Ly said.

"We believe she was closest to the blast," which investigators think may have occurred in the area of the office and motel laundry room, Ly said.

The woman was taken to Integris Baptist Medical Center and the man was transported to Presbyterian Hospital, both in Oklahoma City, said Lara O'Leary, a spokeswoman for the Emergency Medical Services Authority.

Emergency crews evacuated the motel, which had about 40 guests, and electric power was turned off, Ly said.